Responses of Earthworm to Aluminum Toxicity in Latosol
Excess aluminum (Al) in soils due to acid rain leaching is toxic to water resources and harmful to soil organisms and plants. This study investigated adverse impacts of Al levels upon earthworms (Eisenia fetida) from the latosol (acidic red soil). Laboratory experiments were performed to examine the survival and avoidance of earthworms from high Al concentrations and investigate the response of earthworms upon Al toxicity at seven different Al concentrations that ranged from 0 to 300 mg kg-1 over a 28- day period. Our study showed that the rate of the earthworm survival was 100 % within the first 7 days and decreased as time elapsed, especially for the Al concentrations at 200 and 300 mg kg-1. A very good linear correlation existed between the earthworm avoidance and the soil Al concentration. There was no Al toxicity to earthworms with the Al concentration ≤50 mg kg-1, and the toxicity started with the Al concentration ≥100 mg kg-1. Low Al concentration (i.e., <50 mg kg-1) enhanced the growth of the earthworms, while high Al concentration (>100 mg kg-1) retarded the growth of the earthworms. The weight of earthworms and the uptake of Al by earthworms increased with the Al concentrations from 0 to 50 mg kg-1 and decreased with the Al concentrations from 50 to 300 mg kg-1. The protein content in the earthworms decreased with the Al concentrations from 0 to 100 mg kg-1 and increased from 100 to 300 mg kg-1. In contrast, the catalase (CAT) and superoxide dismutase (SOD) activities in the earthworms increased with the Al concentrations from 0 to 100 mg kg-1 and decreased from 100 to 300 mg kg-1. The highest CAT and SOD activities and lowest protein content were found at the Al concentration of 100 mg kg-1. Results suggest that a high level of Al content in latosol was harmful to earthworms.